audio: add channel map selection function

The point is selecting a minimal fallback. The AOs will call this
through the AO API, so it will be possible to add options affecting
the general channel layout selection.

It provides the following mechanism to AOs:
- forcing the correct channel order
- downmixing to stereo if no layout is available
- allow 5.1 <-> 5.1(side) fallback
- handling "unknown" channel layouts

This is quite weak and lots of code/complexity for little gain. All AOs
already made sure the channel order was correct, and the fallback is of
little value, and could perhaps be done in the frontend instead, like
stereo downmixing with --channels=2 is handled. But I'm not really sure
how this stuff should _really_ work, and the new code will hopefully
provides enough flexibility to make radical changes to channel layout
negotiation easier.

1 files changed, 6 insertions, 0 deletions

diff --git a/audio/out/ao.h b/audio/out/ao.h
index 50f121bec2..d908841457 100644
--- a/audio/out/ao.h
+++ b/audio/out/ao.h
@@ -24,6 +24,7 @@
 #include "core/bstr.h"
 #include "core/mp_common.h"
 #include "audio/chmap.h"
+#include "audio/chmap_sel.h"
 
 enum aocontrol {
     // _VOLUME commands take struct ao_control_vol pointer for input/output.
@@ -121,6 +122,11 @@ void ao_reset(struct ao *ao);
 void ao_pause(struct ao *ao);
 void ao_resume(struct ao *ao);
 
+bool ao_chmap_sel_adjust(struct ao *ao, const struct mp_chmap_sel *s,
+                         struct mp_chmap *map);
+bool ao_chmap_sel_get_def(struct ao *ao, const struct mp_chmap_sel *s,
+                          struct mp_chmap *map, int num);
+
 int old_ao_control(struct ao *ao, enum aocontrol cmd, void *arg);
 int old_ao_init(struct ao *ao, char *params);
 void old_ao_uninit(struct ao *ao, bool cut_audio);